Typically, the BIOS displays warning or error messages on the video display in the event of hardware or configuration errors.

However, in some cases the error might be so severe that the BIOS halts immediately or the BIOS might be unable to initialize video. In these cases, it can be useful to determine the last POST task that the BIOS was executing. This is indicated by the value written to port 80.

You can read the port 80 POST codes from the LED on the Sun Ultra 20 Workstation motherboard. The location of this LED is circled in FIGURE C-1. The BIOS post codes are listed in TABLE C-1.